This invention relates to an optical ring system that is composed of multiple nodes connected in the form of a ring, and more particularly to, an optical ring system to process optical signal with multiple wavelengths.
Owing to an increase in amount of communications caused by the popularization of the Internet etc. and the emergence of wideband data service, the enhancement of transfer capacity in backbone network has been desired increasingly. Some of Routers and ATM (asynchronous transfer mode) switches as a device for data service are already provided with a wideband interface at a transfer rate of Gbit/sec, and therefore it is difficult to connect such a device to an existing synchronous network. So, a technology to connect to the network while skipping xe2x80x9ca device to do the time-division multiplexing of low-order group of signal into high-order group of signalxe2x80x9d, an interface of the existing synchronous network, or a WDM (wavelength division multiplexing) technology having a transfer performance more than Gbit/sec to each wavelength has been required.
FIG. 1 shows a prior point-to-point wavelength multiplexing transmission system. First to N-th optical wavelength transmitters 111, 112, . . . , 11N, respectively, convert first to N-th optical signal into optical signal of intrinsic wavelength xcex1 to xcexN, and then output it to an optical wavelength multiplexer 12. The optical wavelength multiplexer 12 multiplexes these optical signal and then outputs it to transmission line 13 connected on the output side. An optical amplifier 14, suitably provided on the transmission line 13, conducts the recovery of deteriorated light in optical signal with wavelength xcex1, to xcexN multiplexed.
An optical wavelength demultiplexer 15 is input optical signal multiplexed from transmission line 16, and demultiplexes it into former optical signal of wavelength xcex1 to xcexN, and then corresponding first to N-th optical wavelength receivers 161, 162, . . . , 16N reproduces the original signal.
Such a point-to-point wavelength multiplexing transmission system as shown in FIG. 1 is equipped with no protection function to protect the transmission of signal when it is subject to a failure such as disconnection of optical fiber to form the transmission lines 13, 16, and malfunction of the optical transmitter/receiver.
The simplest method to provide the optical wavelength multiplexing protection function is to detect a failure at each optical terminal node to provide the protection at multiplexing level of all wavelengths, i.e. in unit of one optical fiber.
FIG. 2 shows an example of optical ring system that employs such a protection method suggested so far. This optical ring system, which is disclosed in Japanese patent application laid-open No. 6-61986 (1994), comprises a four-fiber ring which is of four optical fibers 31 to 34 connected in the form of ring among a master station 21 and first to third slave stations 22 to 24. Of the four fibers, two optical fibers 31, 32 compose work line, i.e. actually-working line, and the remaining two optical fibers 33, 34 compose protection line, i.e. backup line.
The optical ring system in FIG. 2 is not subject to failure. In FIG. 2, master clock output from a clock-supplying device 25, which is disposed in the master station 21, is supplied sequentially from the first to third slave stations 22 to 24.
FIG. 3 shows a case that the work line between the master station 21 and the first slave station 22 in the optical ring system is subject to a failure 41. When the failure 41 occurs on the work line composed of the first and second optical fibers 311, 321, the transmission line is switched so that two optical fibers 331, 341 to compose the protection line in this section can supply the master clock. Then, between the first slave station 22 and the master station 21, the transmission line through the second slave station 23 and the third slave station 24 supplies the master clock like that in FIG. 2.
FIG. 4 shows a case that, between the master station 21 and the first slave station 22 in this optical ring system, not only the work line but also the protection line is subject to a failure 42. When the failure 42 occurs on both the work line composed of the first and second optical fibers 311, 321 and the protection line composed of the third and fourth optical fibers 331, 341, the master clock is supplied through optical fiber 324 in the direction from the master station 21 to the third slave station 24.
Although the transmission of master clock is explained in this example. the first to fourth optical fibers 31 to 34 respectively transmit multiplexing optical signal with multiple wavelengths xcex1 to xcexN, and when optical signal with more than one of the wavelengths is subject to a failure, the switching of transmission line is conducted in like manner described above.
Thus, in the case that, as shown in FIG. 1, optical signal with multiple wavelengths xcex1 to xcexN is multiplexed in one transmission line, even when the transmission line of partial wavelength is subject to a failure, the protection of signal transmission line is conducted by unit of one optical fiber. This means that due to failure of one wavelength, the transmission line of optical signal to the remaining wavelengths has to be switched.
In recent years, optical amplification technology and wavelength multiplexing technology have been developed abruptly. Along with this, the multiplexing number N of optical signal to be transmitted through one optical fiber has increased. Under this background, if even for a failure concerning one wavelength the switching of optical signal to all the remaining wavelengths must be conducted, then optical signal to the wavelengths operated normally may be influenced by an instantaneous shut-off by the switching operation to switch into the protection line. Also, due to the rerouting required when conducting the switching operation of transmission line, delay in transmission of signal occurs, and as a whole the efficiency in use of wavelength band lowers.
Accordingly, it is an object of the invention to provide an optical ring system that when a failure occurs as to only part of wavelengths in point-to-point wavelength multiplexing transmission system, the protection function is conducted to only a wavelength subject to the failure.
According to the invention, an optical ring system, comprises:
a wavelength demultiplexing means to which wavelength-multiplexed optical signal to be sent through an optical fiber from a previous node of multiple nodes composing a ring network is input and in which optical signal with each wavelength assigned to itself is demultiplexed;
an optical ring means which is provided in a predetermined node of the multiple nodes to the each wavelength assigned and which is composed of a failure existence judging means which terminates an overhead of each optical signal with a wavelength demultiplexed by the wavelength demultiplexing means and judges whether a failure occurs in regard to a wavelength in a previous section through which optical signal with the assigned wavelength is sent, and a switching means which, when the failure existence judging means determines the occurrence of failure, selects a path that allows optical signal with the wavelength to be transmitted to the previous node while avoiding the previous section incurring the failure; and
a wavelength multiplexing means which multiplexes optical signal to be output from the optical ring means and then outputs it to an optical fiber connected to a next node composing the ring network.
In this invention, the optical ring means is provided for each wavelength in each node, and after being demultiplexed by the wavelength demultiplexing means, optical signal with a wavelength assigned to the optical ring means is input. The optical ring means terminates the overhead of optical signal assigned and determines whether a failure occurs. In regard to optical signal with the assigned wavelength, when a failure is detected in the previous section, the switching means is controlled to offer the recovery from failure. Optical signal passed through the switching means is multiplexed again with optical signal with the other wavelength by the wavelength multiplexing means when sent to the next node. Thus, the optical ring system of this invention is configured as if the ring network is provided for each wavelength. Therefore, when a failure occurs as to only part of wavelengths in point-to-point wavelength multiplexing transmission system, the protection function can be conducted to only a wavelength subject to the failure.
Also, according to another aspect of the invention, an optical ring system, comprises:
a wavelength demultiplexing means to which wavelength-multiplexed optical signal to be sent through an optical fiber from a previous node of multiple nodes composing a ring network is input and in which optical signal with each wavelength assigned to itself is demultiplexed;
an optical ring means which is provided in a predetermined node of the multiple nodes to the each wavelength assigned and which is composed of a failure existence judging means which terminates an overhead of each optical signal with a wavelength demultiplexed by the wavelength demultiplexing means and judges whether a failure occurs in regard to a wavelength in a previous section through which optical signal with the assigned wavelength is sent, a switching means which, when the failure existence judging means determines the occurrence of failure, selects a path that allows optical signal with the wavelength to be transmitted to the previous node while avoiding the previous section incurring the failure, and a wavelength changing means which changes the wavelength of optical signal to be output from the switching means; and
a wavelength multiplexing means which multiplexes optical signal be output from the optical ring means and then outputs it to an optical fiber connected to a next node composing the ring network.
In this aspect of the invention, the optical ring means is provided for each wavelength in each node, and after being demultiplexed by the wavelength demultiplexing means, optical signal with a wavelength assigned to the optical ring means is input. The optical ring means terminates the overhead of optical signal assigned and determines whether a failure occurs. In regard to optical signal with the assigned wavelength, when a failure is detected in the previous section, the switching means is controlled to offer the recovery from failure. Optical signal passed through the switching means is multiplexed again with optical signal with the other wavelength by the wavelength multiplexing means when sent to the next node. Thus, the optical ring system of this invention is configured as if the ring network is provided for each wavelength. Therefore, when a failure occurs as to only part of wavelengths in point-to-point wavelength multiplexing transmission system, the protection function can be conducted to only a wavelength subject to the failure. In addition, by the wavelength changing means, the output-side wavelength is changed. Therefore, this system can be flexibly applied even to a system where wavelength assignment to optical signal is predetermined.
According to another aspect of the invention, an optical ring system, comprises:
a wavelength demultiplexing means to which wavelength-multiplexed optical signal to be sent through an optical fiber from a previous node of multiple nodes composing a ring network is input and in which optical signal with each wavelength assigned to itself is demultiplexed;
an optical ring means which is provided in a predetermined node of the multiple nodes to the each wavelength assigned and which is composed of a failure existence judging means which terminates an overhead of each optical signal with a wavelength demultiplexed by the wavelength demultiplexing means and judges whether a failure occurs in regard to a wavelength in a previous section through which optical signal with the assigned wavelength is sent, a switching means which, when the failure existence judging means determines the occurrence of failure, selects a path that allows optical signal with the wavelength to be transmitted to the previous node while avoiding the previous section incurring the failure, and a bandwidth narrowing means which narrows the bandwidth of optical signal to be output from the switching means; and
a wavelength multiplexing means which multiplexes optical signal to be output from the optical ring means and then outputs it to an optical fiber connected to a next node composing the ring network.
In this aspect of the invention, the optical ring means is provided for each wavelength in each node, and after being demultiplexed by the wavelength demultiplexing means, optical signal with a wavelength assigned to the optical ring means is input. The optical ring means terminates the overhead of optical signal assigned and determines whether a failure occurs. In regard to optical signal with the assigned wavelength, when a failure is detected in the previous section, the switching means is controlled to offer the recovery from failure. Optical signal passed through the switching means is multiplexed again with optical signal with the other wavelength by the wavelength multiplexing means when sent to the next node. Thus, the optical ring system of this invention is configured as if the ring network is provided for each wavelength. Therefore, when a failure occurs as to only part of wavelengths in point-to-point wavelength multiplexing transmission system, the protection function can be conducted to only a wavelength subject to the failure. In addition, by the bandwidth narrowing means, the bandwidth of optical signal output is narrowed. Therefore, the interaction between optical signals in multiplexing can be reduced, thereby enhancing the efficiency and quality in multiplexing.